Electronic switch



Aug. 30, 1949. P. at SEBRING I ELECTRONIC SWIFTCH Filed March 20, 1945$525 big Paul 5. 5

Patented Aug. 30, 1949 UNITED STATES PATENT OFFICE:

2,480,385 ELECTRONIC swrron Paul B. Sebring. Cambridge, Mass, assignorto the United States of America as represented by the Secretary of theNavy Application March 20, 1945, Serial No. 583,763 3 Claims. (Cl.250-27) This invention relates to an electronic circuit closing deviceand has for its primary object the provision of a device of thischaracter which operates to open and close a circuit between two pointswithout directly affecting either of the points.

Another object of the invention is to provide an electronic switch whichcan be made as effective as a set of contacts in interrupting currentfrom voltages of the order of 100 volts regardless of the polarity ofthe voltage, but which overcomes the disadvantages of a relay in that nomoving parts, or parts subject to corrosion are employed.

Other objects and advantages of the invention will become apparent fromthe following specification taken in connection with the accompanyingschematic diagram which shows one application of the present invention.

Referring to the schematic diagram, the switch of the present inventionis shown applied to control the circuit between points A and B. In theapplication shown it is desired to close the circuit between thesepoints for a definite time interval following the completion of a keyingcycle in another device such as an underwater echo ranging system. Onlythe keying circuit of the echo ranging system is shown, since only thismuch is necessary for an understanding of the present invention. Thekeying circuit involves simply a generator in series with which arevarious relay coils and a key, manually or automatically operated.

The electronic switch of the present invention is connected into thekeying system at point X and includes oscillator Ill of any suitabledesign and operating at any desired frequency sufiiciently removed fromthe operating frequency of the echo ranging system. For example, if theecho ranging system operates at 20 kilocycles, 100 kilocycles has beenfound satisfactory as the operating frequency for the oscillator I0.

The oscillator l includes a triode I I the grid of which is connected topoint K through a capacitor l2 having a discharge path to ground throughresistor l3. The time constant of the RC connecting circuit so formeddetermines the period of closure of the switch as will be hereinafterexplained. I

The oscillator circuit shown is a conventional Hartley circuit, but itis obvious that oscillators of other types may be used. Such oscillatorsinclude the colpitts, the ultraudion, and other circuits which are wellknown to those skilled in the art.

A part of the tank circuit of oscillator I0 is constituted by a coil l5which acts as the primary of two transformers the secondaries of whichare coils H and IS. The secondaries are preferably wound on the sametoroidal form as the primary IS. The output of each secondary coil isrectified and filtered and applied to the grid of a triode as acontrolling bias. Rectification of the transformer output takes place indiodes 2| and 22 and the'associated filter circuits are designatedgenerally 23 and 24, while the controlled triodes are numbered 25 and 26in the schematic. The output of the oscillator is such that when theoscillator is operating, suficient voltage is induced in coils I! and I9to completely block the triodes 25 and 26 so that there is effectivelyan open circuit between points A and B.

The filter units 23 and 24 operate at the frequency Of theoscillatorlll, and may be quite small because of the high frequency. Itis desirable that the shunt capacitors of these filters dischargequickly so as not to introduce an appreciable time delay. The shuntresistance should be made as low as possible without unduly reducing theoutput voltage of the filter.

It will be seen that the triodes 25 and 26 are oppositely connected sothat the polarity of the voltage presented to the switch is of noimportance in the action of the switch, which will conduct in eitherdirection when closed.

The triodes 2| and 22 may, of course, be replaced by other types ofrectifiers such as the copper oxide rectifier or the germaniumrectifier.

The operation of the device may be summarized by considering a, typicalcycle of an associated echo ranging system in which a short pulse ofsound is emitted, followed by a period in which it is desired to close aswitch for a predetermined interval. A relay could be used with a propertime delay but such apparatus has numerous objections which areunimportant here. It is desired that all connections remain undisturbedand also that the switch be completely free of ground so that the gridof each triode 25 and 26 must be biased oif with respect to its owncathode whenever the switch is to be opened. In the present inventionthe isolation from ground is accomplished by using the voltage fromsecondaries l1 and I9 as bias voltages as above stated. Having madeclosure of the switch dependent solely on the conducting condition oftriodes 25 and 26 and hence the voltage in secondaries I! and I9, itremains only to control the oscillator I0 in order to control theswitch.

, If the oscillator is operating, a voltage is induced in each of thesecondaries i1 and I9 and the switch, as above stated, is open, whileif, for any reason, the oscillator should be cut off or its actionstopped, the bias Voltage on the grids of triodes 25 and 26 willdisappear. The tubes then conduct and the switch would be in its closedstate permitting current flow between points A and B.

In the application of the invention shown in'the schematic diagram theoscillator is controlled by the keying circuit in the following manner.If it is considered that the key has been open for some time and theoscillator is oscillating, capacitor it will have a potential across itsterminal which is equal to the difference in voltage between thenegative supply to the keying circuit, which is shown as thegenerator'Gen and thecoil marked Relay coil, and the negative voltagebuilt up across resistor 13 due to the grid current of the oscillator.If the key is suddenly closed, point X in the keying circuit instantlyassumes ground potential and, since the voltage across capacitor 42cannot change instantaneously, positive' voltage is fed to the grid oi"the oscillator triode H which merely serves to increase temporarily thegrid current of the oscillator but does not stop the oscillation of thecircuit, The increased grid current serves also to quickly dischargecapacitor !2 so that the potential across this capacitor becomes onlythat due to grid current of triode l! through resistor I3. If the key issuddenly opened, point X becomes immediately negative to ground by thevoltage of the generator. Since again the potential across capacitor !2cannot change instantly but must build up due to current flow throughresistor l3, a high negative voltage, sufiicient to out 0113 the tube,is applied for some time to the grid of triode ii in the oscillatorcircuit thus blocking the oscillator for a period depending on the timecons nt of the charging circuit of capacitor 12. This time constant, canof course, be set at any desired value so that the on-off period of theoscillator is subject to selection. It will also be noted that thecontrolling circuit for the oscillator may take any desired form withoutaltering the fact that the real switching between points A and B isaccomplished as separately and efliectivcly as could be done by a relaywithout thedisadvantages attending this type of equipment and withoutaltering in any way the connections between these points.

It is obvious to those skilled in the art that the generator Gen may bereplaced by abattery or other suitable source of voltage. It is alsoobvious that in this application the coil relay coil acts only as acurrent limiting resistance and may be replaced by resistance ofsuitable value. The point r is provided as shown with a by-passcondenser of small capacity to keep high frequency current from theoscillator out of the power source and other circuits where it wouldinterfere with proper operation of such circuits.

In the application of the invention to echoranging apparatus it isordinarily desirable to arrange the switch so that it is either on oroff."

second electronic tube having an anode, a cath- 'ode';"and a controlgrid, means connecting the cathode of said first tube and the anode ofsecnd tubeto one of said terminals, and means connecting the anode ofsaid first tube and the cathode of said second tube to the other of saidterminals; a normally operative electronic oscillator comprising aninductance paralleled by capacitance; a pair of output coils inductivelyrelated to said inductanceto each receive therefrom an'alternatingcurrent voltage of a magnitude exceeding the cutoff bias ofthe said electronic tubes, a unidirectional conducting device connectedwith each of said output coils. individualized filter me'ansconnected tosaid unidirectional conducting device to produce a direct currentvoltage at the output of each'of said individualized filter means; meansfor-applying one of said direct current voltages between the grid andthe oathode of' said'first electronic tube and means for applying theother of said direct current voltages between thelgrid and the cathodeof said other electronic tube, whereby said first and second electronictubes are rendered non-conducting when said oscillator is operative; andmeans to render said electronic oscillator non-oscillatory for apredetermined period following the actuation ofsaid means.

2, An electronic switch having a pair of terminals comprising; a firstelectronic tube having an anode, a cathode, and a control grid, a secondelectronic tube havin an anode, a cathode, and a control grid,means'connecting the anode of said first electronic tube and the cathodeof said second"electronic tube to one'of said terminals, and meansconnecting the cathode of said first electronic-tube and the anode ofsaid second electronicitube to the other of said terminals; anormallyoperative electronic oscillator comprising a third electronictube having an anode, a cathode and a grid-and an'inductance paralleledby capacitance electrically associated with said third electronic tubeto produce sustained oscillation; a pair of output coils inductivelyrelated to said inductance toeach receive therefrom analternatingcurrent voltage of a magnitude exceeding the cut-'ofi bias'ofsaid electronic tubes, an individualized unidirectional conductin deviceconnected with each-of, said output coils to rectify said alterhatingcurrent induced in said coils, individualized filter means connectedwith said rectifying means to produce a direct current voltage at theoutput of each filter; means connecting one of said individualizedfilter means to said first electronic tube to apply said direct currentvoltage betweeniithegridand the cathode of said first electronictube andmeans to connect the other of. said individualized'filter means to saidsecond electronic tube to apply said direct voltage between the-grid andthe cathode of 'saidsecond electronic tube, whereby said electronictubes are rendered non-conducting when said oscillator is operative;a'source of direct current voltage, a capacitor-resistance circuitconnected to the: grid of said third electronic tube, means for applyinga negative bias from said source of direct current through saidcapacitor-resistor circuit to the grid of said tube to render saidoscillator inoperative, said negative bias being applied for a timeinter val determined by the charging rate of said capacitor-resistorcombination.

3. An electronic switch havin a pair of ter minals, comprising; a firstelectronic tube having an anode, a cathode, and a control grid, a secondelectronic tube having an anode, a cathode, and a control grid, meansconnecting the anode of said first electronic tube and the cathode ofsaid second electronic tube to one of said terminals, and meansconnecting the cathode of said first electronic tube and the anode ofsaid second electronic tube to the other of said terminals; a normallyoperative electronic oscillator comprising a third electronic tubehaving an anode, a cathode, and a grid, and an inductance paralleled bycapacitance electrically associated with said third electronic tube toproduce sustained oscillation; a pair of output coils inductivelyrelated to said inductance to each receive therefrom an alternatingcurrent voltage of a magnitude exceeding the cutoff bias of saidelectronic tubes, an individualized unidirectional conducting deviceconnected with each of said output coils to rectify said alternatingcurrent induced in said coils, individualized filter means connectedwith said rectifying means to produce a direct current voltage at theoutput of each filter; means connecting one of said in dividualizedfilter means to said first electronic tube to apply said direct currentvoltage between 6 the grid and the cathode of said first electronic tubeand means to connect the other of said individualized filter means tosaid second electronic tube to apply said direct voltage between thegrid and the cathode of said second electronic tube, whereby saidelectronic tubes are rendered nonconducting when said oscillator isoperative; a tapped grid resistor connected to the grid of said thirdelectronic tube, a source of direct current voltage, a capacitorconnected between the tap on said grid resistor and the negative side ofsaid source of direct current voltage whereby said capacitor is normallycharged, and means for discharging said capacitor, whereby said negativepotential of said source of direct current is applied to the grid ofsaid third electronic tube thus rendering said electronic oscillatornon-oscillatory during the chargin time of said capacitor.

PAUL B. SEBRING.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS

